Multi-Position Work Tables

ABSTRACT

A compact height adjustable work station utilizes a unique combination of support arms and linkages to achieve greater strength and a greater range of tabletop height adjustment from a smaller form factor than is found anywhere in the industry. The method for adjusting the work surface height is user operated and pressure assisted whereby the user requires a minimal effort to physically lift or lower the work surface to the desired tabletop height. The pressure assist can be variably located to counterbalance different tabletop weights. For automatic counterbalancing, an elongated extensible gas spring piston-cylinder is adapted to be locked in any of its continuous range of infinite adjusted positions. Manual unclamping frees the counterbalancing gas spring for readily changed, manual tabletop height level adjustment. A mid-range level or a high tabletop level may be achieved, adjusted by unclamping and minimum manual force.

FIELD OF THE INVENTION

This invention relates generally to tables in the furniture field and,more specifically, to ergonomically designed office and industrial workstations.

The invention provides height adjustable multiple-position worktablelevels producing ergonomic benefits to workers of various size whilethey are performing various work tasks. Research has shown that adaptinga work station to the reach and viewing needs of a worker increasesproductivity and reduces the occurrence of injury.

The preferred embodiments of the invention are extremely economical tomanufacture and readily operated by the user to achieve prompt andefficient movement of the tabletop between an infinite number ofdifferent level positions.

Mechanical and hydraulic jacks have been suggested, but they oftencompel the user to provide exhausting hand-cranking or carefulmonitoring of electrical pump controls. Moreover, such jacks introduceundesirable weight and considerable extra cost, making suchjack-actuation undesirable for many users.

It is, therefore, the principal object of this invention to provide aheight adjustable work surface that will move down to accommodate thesmallest seated individual and then rise up to accommodate the talleststanding worker.

It is also an object of this invention to create a new height adjustablework station that will utilize a unique combination of cooperatingsupport arms and linkages to provide greater strength and achieve agreater range of adjustment from a smaller form factor than couldnormally be accomplished.

It is another object of this invention that the work station is usercontrolled and manually operated and that the work surface adjustsquickly up and down without the use of expensive electric motors orcumbersome manual cranks.

It is a further object of this invention that the motion of the supportarms and linkages is pressure assisted by a pressurized gas pistoncylinder to counterbalance the weight of the tabletop.

It is a still further object of this invention that the pressure assistcan be variably located to counterbalance different tabletop weights.

It is another feature of this invention that the work station providesmaximum legroom for seated positions and minimum use of office space inthe standing position.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description taken inconnection with the accompanying drawings(s) in which:

FIGS. 1A, 1B, 1C and 1D are successive schematic side elevation views ofthe first embodiment of the invention, with the tabletops shown elevatedto successively greater height levels;

FIG. 1E is an enlarged schematic side elevation view of the firstembodiment, clearly showing the component parts of the mechanism;

FIG. 1F is an exploded elevation view of the component parts of thefirst embodiment;

FIGS. 2A, 2B, 2C and 2D are comparable successive schematic sideelevation views of the second embodiment of the invention, with thetabletops shown elevated to successively greater height levels;

FIG. 2E is an enlarged schematic side elevation view of the secondembodiment, clearly showing its component parts;

FIG. 2F is an exploded elevation view of the component parts of thesecond embodiment,

FIGS. 3A, 3B, 3C, 3D, 3E and 3F are successive schematic side elevationdiagrams illustrating the cooperative interaction of the human user withthe first embodiment of the invention, shown in its successive raisedand lowered tabletop height levels;

FIGS. 4A, 4B, 4C, 4D, 4E and 4F are successive schematic side elevationdiagrams illustrating the cooperative interaction of the human user withthe second embodiment of the invention showing its successive raised andlowered tabletop height levels;

FIGS. 4G, 4H, 4I and 4J are schematic side elevation diagrams of amodified version of the second embodiment. FIGS. 4G and 4I show thelowest and the highest tabletop levels of this version, and FIGS. 4H and4J are corresponding respective lowest and highest level diagramsshowing the linkage of this modified second embodiment with the tabletopremoved for clarity.

FIG. 5 is an enlarged schematic side elevation diagram of the mechanismof the second embodiment, showing the virtual centers of rotation of thetabletops rear rim and its upper support link, both positionedrearwardly in space behind the mechanism by a substantial distance.

FIGS. 6, 7 and 8 are successive schematic side elevation diagrams of themechanism of the second embodiment, showing its component parts in itslowest, middle and highest tabletop levels.

FIGS. 6A, 7A and 8A are corresponding successive schematic sideelevation diagrams of the second embodiment, showing the successivechanges in the shapes of the two parallelograms delimited by its pivotpoints during its transitions between height levels,

FIG. 8 is a corresponding collection of schematic side elevation viewsof the same device shown in the same four different positionsillustrated in FIGS. 3 and 4 as well as two additional positions 5 and6. These diagrams of FIG. 8 illustrate the user's manipulation of thesimple controls of the worktable to move it from its lower level inposition 1 toward a mid level position shown in FIGS. 2 and 3, andthence toward an upper position shown in positions 4 and 5 and finallyto return it to the lower position of FIGS. 1 and 6;

FIGS. 9A and 9B are two different views of the pressurized gas cylindervalve control cable assembly incorporated in the preferred embodimentsof the present invention, FIG. 9A being a side view of the cableassembly and FIG. 9B being a front view of the same component;

FIG. 9C is a perspective side view of a pressurized gas springpiston-cylinder assembly;

FIG. 9D is a schematic cross-sectional diagram of a pressurized gasspring piston-cylinder assembly, a Stabilus BLOC-O-LIFT® “gas spring”;

FIGS. 10A, 10B, 10C and 10D are four comparison charts, showingoperation characteristics of the device;

FIGS. 11, 12, 13 and 14 illustrate a third preferred embodiment of theinvention;

FIG. 11 is a perspective corner elevation view of this different form ofthe worktable in its lower position, supporting a desk top computer onits upper worktable surface;

FIG. 12 is a corresponding view showing the same table at a higherworktable height above the height shown in FIG. 11;

FIG. 13 is an enlarged side perspective view of the same device in itsupper position corresponding to that in FIG. 12;

FIG. 14 is a perspective bottom plan view of the third embodiment of theinvention in which the pivoted linkage legs and the gas springpiston-cylinder are more clearly illustrated.

FIGS. 15A, 16A and 17A are successive schematic bottom plan diagrams ofthe elevating linkage of the third embodiment, shown respectively in thelowest, a middle and the highest positions of the tabletop heightlevels;

FIGS. 15B, 16B and 17B are successive side elevation diagrams of themovable legs and tabletop of the third embodiment, shown respectively inthe lowest, a middle and the highest positions of the tabletop heightlevels,

FIG. 18A is an enlarged bottom plan diagram of the tabletop undersideportion of the elevating linkage of the third embodiment, in its highestlevel position shown in FIGS. 17A and 17B, with a bell crank having twoequal length arms, and

FIG. 18B is an enlarged bottom plan diagram similar to FIG. 18A,showing-a bell crank having arms of different length.

BRIEF SUMMARY OF THE INVENTION

The invention comprises a method and apparatus for adjusting the heightof a tabletop work surface by selecting among an infinite number oflevel positions.

The method for adjusting the tabletop work surface height is manuallyuser operated and pressure assisted, whereby the user provides minimaleffort to physically lift or push down the work surface to the desiredtabletop height.

The invention incorporates a method and apparatus to variably locate thepressure assist device to specifically counterbalance different tabletopweights.

The apparatus is a unique combination of cooperating support arms andlinkages that maintain the work surface in a horizontal positionthroughout its range of motion. The unique linkage provides betterstrength geometry than other linkage designs and pivots about virtualcenters in imaginary space to create a smaller overall form factor thattakes up less space in the workplace.

BEST MODES FOR CARRYING OUT THE INVENTION The First Preferred Embodiment

In the first preferred embodiment, shown in FIGS. 1A-1E, and 3A-3F, atabletop work surface adjusts up and down and locks in position bycontrolling the movement of a pressurized gas spring piston-cylinder.The tabletop 20 is supported in a horizontal position throughout itsrange of motion by a linkage 21, a series of articulating linkage armspivotally mounted on a column 22 upstanding from the rear of the tablebase 24. A pressurized gas spring piston-cylinder 55 is mounted betweenthe linkage 21 and the table base 24 (FIG. 1E). Opening and closing avalve 48 on piston-cylinder 55 (FIG. 9A) determines the movement of thegas piston and unlocks or locks the position of the linkage.

The tabletop 20 adjusts from a low (seated) work height, FIGS. 1A and 3Ato a standing work height, FIGS. 1D, 1E and 3D, to accommodate differentsize individuals performing various work tasks. The tabletop is adjustedmanually by the user to the desired position. The amount of manualeffort required to move the tabletop up and down is reduced to a minimumby the gas piston-cylinder which is pressurized to counterbalance thetotal weight of the tabletop and the objects on the tabletop.

First and Second Embodiments

Comparison of FIGS. 1E and 2E shows that tabletop 20 is supported inboth the first and the second preferred embodiments by a pivoted linkage21, which itself is pivotally mounted on column 22, upstanding from base24.

In each embodiment a gas spring piston-cylinder assembly 55 has its endspivotally connected to column 22 and to linkage 21.

The pivotally connected components forming linkage 21 are very similarin both the first and the second preferred embodiments. This isconfirmed by comparing the exploded views of FIG. 1F and FIG. 2F, wherethe various comparable components are arrayed side by side in these twoFIGURES. The pivoted interconnections of each of these linkagecomponents with the next is clearly shown in the assembled views ofFIGS. 1E and 2E, and their articulated movement is shown in FIGS. 3A-3F.

Thus, for the first embodiment, a central member is the cantilever arm29, shown to be U-shaped in FIG. 1F, having rear pivot point 31, joiningit to column 22, and a front pivot point 32 joining arm 29 to theunderside of tabletop 20 via a top plate 33.

A bell crank 34 is pivotally joined at a central point to the cantileverarm 29 near its front end by a pivot 36.

An upper link 37 has an upper end joined to a rear point of top plate 33by a pivot 38, and a lower end pivotally joined to an upper rear end ofbell crank 34 by a pivot 39.

A forward link 40 has a front end pivotally joined to the lower end ofbell crank 34 by a pivot 41, and a rear end pivotally joined to column22 by a pivot 42 at a point substantially below pivot 31.

Gas spring piston-cylinder 55 has its upper end pivotally joined by apivot 54 to an upper bridge plate 56 having a rear end anchored to pivot31 on column 22, and a forward end anchored to a central point oncantilever arm 29, making bridge plate 56 integral with arm 29.

Piston-cylinder 55 also has its lower end pivotally joined by a pivot 53to a bed plate 57 anchored to the lower end of column 22.

The pivoting articulation of all of these pivotally connected componentsof linkage 21 is illustrated in the six successive diagrams of FIGS. 3Athrough 3F.

Pivoted Components of Second Embodiment

As shown in FIGS. 2E and 2F, the same components are connected in muchthe same fashion in the second preferred embodiment as they are in thefirst preferred embodiment, and the pivoting articulation of thesecomponents of linkage 21 is shown in the six successive diagrams ofFIGS. 4A through 4F, and in FIGS. 6, 7 and 8.

Accordingly, the foregoing description of the linkage components of thefirst preferred embodiment is equally applicable to those of the second,and the corresponding components and pivot points have been given thesame reference numerals in the FIGURES.

Cantilever arm 29 is V-shaped and bell crank 34 is generally triangular,but these do not change their function or cooperation.

Operation of the Gas Spring Piston-Cylinder

When the gas spring piston-cylinder 55 is ideally pressurized for thetotal weight of the tabletop, opening the control valve 48 will allowthe tabletop to “float” with minimum hand pressure up and downthroughout its range of motion. Closing control valve 48 locks thepressurized gas piston in its then current extension position. Theamount of gas pressure is selected to counterbalance the total tableweight.

The preferred pressurized gas spring piston-cylinder assembly 55employed in the preferred embodiments of the invention is the Stabilusrigid blocking BLOC-O-LIFT® gas spring, sold by Stabilus Inc. ofGastoria, N.C. 28052-1898. BLOC-O-LIFT® gas springs raise loads with anaccurately tuned extension force and application-specific dampeningwhile ensuring user-friendly movement sequences. In addition,BLOC-O-LIFT® gas springs can be blocked in any position, with springingor rigid blocking in the extension or compression direction depending onthe design, according to the Stabilus catalog. A schematiccross-sectional diagram of this device is shown in FIG. 9D.

This gas piston-cylinder assembly counterbalances the weight of thetable near the midpoint of its range of levels, and the rigid blockingBLOC-O-LIFT® gas spring can be blocked in any position in its range.Variable blocking is produced by the valve 48 integrated into thepiston, which separates both pressure chambers gas-tight. When valve 48is closed, blocking the gas exchange between the two pressure chambers,the BLOC-O-LIFT® gas spring is blocked, and the table level is locked.The valve 48 closes automatically when the valve tappet is releasedexternally.

At any point in its movement when the control valve 48 is closed, thegas spring piston-cylinder 55 is thus locked in position, converting thegas spring 55 into a rigid link between its end pivots 53 and 54. Asimple unclamping lever 26, FIGS. 1E, 2E and 8A, controls the closing ofthe valve 48 via a “camera-shutter style” cable 50 to lock the tabletopin position. FIGS. 3A-3F show how the depicted user, operating theunclamping means, the release control actuator (a push button orgrippable paddle lever) 26, acting through the flexible cable 50, locksthe table in various positions or unlocks the gas piston-cylinder 55 formovement to and from various positions. The components of a typicalpressurized gas piston-cylinder 55 controlled by lever 26 are depictedin FIG. 9D.

Variable (Lift) Pressure Assistance from Fixed Pressure CounterbalancingSpring

The gas springs or air spring piston-cylinder assemblies of thisinvention are lockable at any one of an infinite number of pistonextension positions. The somewhat similar gas-charged trunk lid liftersor hood lifters for automobiles move the lid or hood up slowly to itsuppermost position counterbalancing its weight. The user's manualclosing of the trunk lid or hood adds a few extra pounds of force to theactual weight, overcoming the counterbalancing and slowly lowering thelid or hood to its lowest closed position.

Such lifters cannot be locked in any intermediate position.

The piston-cylinder assemblies 55 of this invention are designed to movethe tabletop 20 buoyantly to a floating position, in the mid region ofits raising or lowering range, when the lever 26 is actuated to unlockassembly 55. While lever 26 is actuated the user can slowly raise orlower the tabletop 20 to any selected new position by applying slightupward lifting or downward force, making its level adjustment easy byminimizing the adjustment force required.

Actuator 26 may be located on the underside of the tabletop at a centralposition under its front rim, as in FIG. 14, but it is preferable torequire both of the user's hands, by positioning lever 26 under the siderims near the front rim of the tabletop 20 or 61, as indicated in FIGS.1E, 2E, 4A-4F, 15A, 16A, 17A, 18A and 18B.

Levers 26 are essential to tabletop movement because engaging thecontrol lever 26 to release the locking valve 48 requires the user'shands to be in contact with the table, gripping the front portions ofboth side rims.

Thus, if the table were to rise or fall at a speed or direction wherethe user were to fear losing control, the user could simply release hisgrip on the control lever 26 or even remove his hands from the table,and the table would automatically lock and stop motion, a “fail safe”result.

It can be appreciated that the amount of gas pressure and the tabletopweight are dependent upon each other. If a fixed gas cylinder chamberpressure were to be specified for a given tabletop weight and the totaltabletop weight were to increase, the tabletop would not “float”buoyantly in the user's hand as easily—requiring greater manual effortto raise the tabletop, and conversely less effort to lower it.

Generally the tabletop weight and the gas pressure are matched to theknown use of the tabletop, i.e. as a light assembly table or as aheavier computer work station. However when the tabletop weight ispurposely changed for a different task, the gas spring (with a fixedpressure) can be re-positioned to exert more or less counterbalancingforce to compensate for more or less tabletop weight.

For positioning the gas pressure cylinder, preferably a StabilusBLOC-O-LIFT® gas spring, careful consideration of force, weight andstructural vectoring need be taken into consideration. When the tablestart position (lowest position) FIG. 1A is below a hinge point 31 on afixed column 22, the table weight to be counterbalanced is less than theactual table weight as the base-column structure supports a vectoredcomponent portion of the actual weight. For instance, if the tableweighing 100 pounds were positioned at 45 degrees below the hinge point,fifty percent of the weight would be born by the base-column structure22-24, presenting only half the weight to be counterbalanced by the gaspressure cylinder 55. However, as the tabletop rises to a level evenwith the hinge point 31 the table presents its full 100-pound weight tobe counterbalanced by the gas pressure cylinder 55.

Conversely, the gas pressure cylinder counterbalancing force is notdependent on gravity—its force is directly related to its piston strokeposition. Gas cylinder pressures generally will have a range of forceratios of 1.4 to 1.0—i.e., fully compressed a gas cylinder will exert40% greater force than when its piston is fully extended.

The weight of the table—constantly varying by the effect of gravity andstructural vectoring—is opposed by a gas cylinder pressure thatdiminishes constantly in a linear progression. This presents problemswhen the designer wishes to use the linearly diminishing gas pressure tocounterbalance table weights that rise and fall in relation to theeffect of gravity acting on the articulated linkage 21.

Referring now to the schematic diagrams of FIGS. 1A and 10A, a tableweight of 100 pounds is positioned 30 degrees below the hinge point 31in the lowest adjusted position of the first preferred embodiment. Thegas pressure cylinder is fully compressed. Referring to FIG. 10A, it canbe seen that in this lowest position the tabletop 20 has one third ofits weight supported by the base-column structure and the weightpresented to be counterbalanced by the gas pressure cylinder is 66.6pounds. The fully compressed gas pressure cylinder has 100% of its forceavailable to lift 67% of the table weight. Thirty degrees of travel upbrings the table horizontally even with the hinge point 31 (FIGS. 1B and3A) and increases the table weight to one hundred pounds and thebase-column structure contributes zero to bear weight. The gas pressurecylinder has extended 40% of its stroke and depleted its force to 60% ofits potential. In viewing the chart, FIG. 10A, while the weight hasincreased by 34%—the gas pressure cylinder force has decreased 40%.

If attempting to use the gas pressure cylinder 55 as a counterbalance toneutralize the effort to move the tabletop, a different relationship ofgas pressure cylinder location and table position must be realized. Thetable is affected by its position in relation to gravity. The gascylinder is not affected by gravity—vector forces only affect the gascylinder where force is shared with structure. It is important to usethe structure to mechanically disadvantage the gas cylinder when thetable weight is presented at a lower value and allow the gas cylinder tobe less disadvantaged when the table weight increases.

Referring now to FIG. 10B, when the table-top is located down 30 degreesas in FIG. 10A (and one third of its weight is reduced) the gas pressurecylinder is located down 45 degrees against the same base-columnstructure as bears the weight of the table. When the table has rotatedto 30 degrees travel and is fully horizontal at full weight, the gaspressure cylinder is 15 degrees from its neutral position—i.e. one sixthof its force is still being shared with the structure. Comparing thecurves of the actual force output in FIGS. 10A and 10B, it can be seenthat repositioning the gas pressure cylinder as in FIG. 10B has causedthe force to be more equal to the table weight in the beginning oftravel and to become greater in the latter portions of travel. Changingthe mount points and pressure amount of the gas pressure cylindercompared to the known position and weight of the tabletop caneffectively determine how the table will rise and descend as influencedby the gas pressure cylinder.

Fine Tuning the Counterbalancing Force

Turning now to FIG. 10C, tabletop 20 starts from its lowest position(FIG. 1A) down 30 degrees from hinge point 31. The fully compressed gasspring 55 is pivotally joined to linkage 21 at 40 degrees below“neutral”, producing gas spring force exceeding the component oftabletop weight to be counterbalanced over the entire range of tabletoplevel positions.

As shown in FIG. 10D, fine tuning the compressed gas spring pivotmounting on the linkage 21 by reducing 40 degrees below neutral down to35 degrees below “neutral” brings the excess gas spring counterbalancingforce even closer to the component of tabletop weight to becounterbalanced over the range of tabletop positions.

As the linkage 21 articulates, moving through the positions of FIGS. 4Athrough 4C, the gas piston-cylinder 55 becomes longer as the pistonextends from the cylinder. As seen in these FIGURES and in FIG. 2E,moving end 54 pivoted to cantilever arm 29 at 54B, describes an arcabout rear pivot point 31 on column 22.

When the axis of piston-cylinder 55, from pivot point 53 to pivot point54, is at 90° to the radius of that arc, from pivot point 54 to rearpivot point 31, this corresponds to the “neutral” tabletop level, wherethe components of tabletop and cargo total weight to be counterbalancedis maximum.

If the fully compressed piston-cylinder's moving end pivoted at 54Bdefines a radius to pivot point 31 angularly rotated below the neutralradius by 35°, substantially as suggested by FIG. 2A, the gas spring'smaximum counterbalancing force is disadvantaged until the neutraltabletop level is reached, producing the optimum match of weight tocounterbalancing force shown in the diagram of FIG. 10D.

Alternative pivot bores where gas spring terminal pivots can be mountedare shown as bores 53 and 53A, 54 and 54A in FIGS. 1E, 1F, 2E and 2F.Selection among these alternatives allows the user to achieve the finetuning 2E desired.

A diagram of the neutral position of a gas piston-cylinder 52 appears inFIG. 18A. There, moving end 48 of the piston-cylinder, guided by theouter arm of the bell crank 69, describes an arc 67 about the centralpivot 79 of bell crank 69. A line drawn from the piston-cylinder's fixedend pivot 82 (on the underside 67 of tabletop 61) is tangent to arc 67at a point 68, where radius 68-79 is perpendicular to line 68-82, whichnearly coincides with the central axis of gas spring 52. Radius 68-79thus represents the neutral position of the Bloc-O-Lift in FIG. 18A, andthe acute angle 37.5° between radius 79-48 and neutral radius 79-68indicates an angle greater than the 90° neutral position. The angles 30°and 45° in FIG. 10B, angles 30° and 40° in FIG. 10C, and angles 30° and35° in FIG. 10D all represent radii whose angles are deducted from the90° angle of the neutral radius, before the piston-cylinder has extendedto the neutral position. If the moving end 48 of the piston rod is belowneutral by 30° or 45°, this reduces the moment arm of thecounterbalancing force, thus disadvantaging the gas spring.

Upright Gas Piston-Cylinder and Linkage Location Points

The gas piston-cylinder 55 fixed-end and moving-end mount pivot points s53, 53A, 54, 54A and the corresponding linkage and table base-columnmount or pivot points are carefully positioned in relationship to eachother.

Referring now to FIG. 2B, a height adjustable table representing thesecond preferred embodiment of the present invention and adjusted withthe cantilever arm 29 in a horizontal position, with its two terminalpivot points 31 and 32 on the same horizontal plane. It can be seen inFIGS. 2B, 2E, 5, 7 and 8 that the moving-end 54 of the upright gaspiston-cylinder 55 is mounted to the cantilever linkage arm 29, and thefixed-end 53 of the gas piston-cylinder 55 is mounted to the tablecolumn 22. In FIG. 2E the moving-end 54 of the gas piston 55 is mountedto the linkage arm at point 54B at a specific distance from the pivotpoint 31 to exert 100% effort to raise a tabletop weight. To reduce thelifting force of the gas piston-cylinder 55, as shown in FIGS. 2E and2F, the moving-end 54 can be repositioned at a lesser distance frompivot point 31 at location 54A producing a decreased mechanicaladvantage.

Altering the mechanical advantage can be best understood byforce-ratios. In FIG. 2B, if the distance between the pivot point 31 andthe table pivot point 32 were 12″ and the weight on the tabletop were 10pounds, the cantilever support arm 29 would be holding 10 foot poundswhen in a horizontal position. If the moving-end 54 of the gaspiston-cylinder 55 were located at a distance of 6″—the lifting forcerequirement of the pressurized gas piston-cylinder from half thedistance would be doubled (a 2 to 1 force-ratio) requiring 20 footpounds of piston lifting pressure.

Referring now to FIG. 2E, if the moving-end 54 of the gas piston 55 werefurther relocated, and the distance were now reduced to 3″ from thepivot point 31, the lifting force of the pressurized gas piston-cylinder(attempting to lift the same 10 pounds from now one quarter thedistance) would be a 4 to 1 force-ratio—requiring 40 foot pounds ofpressure.

However, gas pressurized pistons have a fixed gas pressure so when thegas piston (pressurized to lift 20 pounds as in FIG. 1E) isrepositioned, the same (fixed lifting pressure) piston can only lift 20pounds—not the required 40 pounds. Since the piston pressure is fixed,the only way the piston could lift the tabletop would be if table weightwere reduced from 10 pounds to 5 pounds.

Hence it can be appreciated that the gas piston-cylinder 55 (with afixed lifting pressure) can be positioned and repositioned at anincreased or decreased mechanical advantage to compensate for increasingand decreasing total tabletop weights.

Further to the method of relocation of the gas piston mount points, thelift characteristics of the gas piston can be fine-tuned by addressingwhat portion of the existing stroke is utilized. Referring again to FIG.1E, to the extent that the gas piston fixed-end 54 is moved inwardstowards the pivot point 31 and the fixed-end mount point 53 remains thesame, the gas piston moves through a correspondingly shorter strokedistance to lift the linkage via the cantilever arm through the samerange of motion.

Depending upon the distance from the moving-end 54 to where thefixed-end 53 is relocated to the table column 22, e.g. at mount point53A (FIG. 1E), which is further, or point 53 (FIGS. 1E and 1F), which iscloser, the stroke portion utilized will be determined to be at thebeginning of piston travel (when the piston exerts the greatest force)or at the mid or end of its piston travel (when the piston exertscorrespondingly less force). Hence it can be further appreciated that agas piston of any given fixed pressure (when repositioned closer to thepivot point) has a shorter stroke requirement. By locating the fixed-endat differing length locations to use different portions of the stroke,it can effectively adjust the lifting power characteristics of the gaspiston stroke to also relate to varying total tabletop weights.

It can be lastly appreciated that instead of a number of different gaspiston mount points on the table base and linkage arms, a sliding mountmechanism (or other means to variably locate the two mount points) canbe utilized.

Forwardly Projecting Air Spring Piston-Cylinder

In FIGS. 4G, 4H, 4I and 4J, a modified second embodiment of theinvention is shown, with the substantially upright air springpiston-cylinder 55 replaced by a forwardly projecting air springpiston-cylinder assembly 51.

Piston-cylinder 51 is also preferably a Stabilus Block-O-Lift lockinggas spring, having end points 53 and 54 for mounting it to the otherlinkage components (FIGS. 9C, 9D, 4G-4J).

In FIGS. 4G and 4H, at the lowest level position of the tabletop 20,forwardly projecting air spring 51 is tilted downward, among thecompactly associated components of linkage 21.

In FIGS. 4I and 4J, at the highest level position of tabletop 20, theextended gas spring 51 has pivoted upward to tilt upwardly, with its endpoints 53 and 54 respectively pivotally connected to the column 22 andto the cantilever arm 29, still positioned among the compactlyassociated components of linkage 21.

It can be understood from FIGS. 4G to 4J that the location and operationof the gas pressure piston-cylinders are unrelated to their orientationin relation to gravity, but they are still relatively affected bystructural vectoring. A forwardly projecting near-horizontallypositioned gas spring 51 is mounted in the second preferred embodiment,to produce the same range of motion and neutral buoyancy lift force ascompared to the upright and near vertical gas springs 55.

In addition, when FIGS. 4G-4J are compared to FIGS. 6-8, for example,the absence of the upright gas spring 55 and its replacement by theforwardly extending gas spring 51 among the other components of linkage21 creates a more streamlined and efficient column 22, with all of thelinkage 21 including gas spring 51 forming a single articulatingassembly directly under the tabletop.

Gas spring piston-cylinder assemblies 51 and 55 perform similarfunctions with efficiency, and both provide the same opportunities forfine tuning their counterbalancing force, as illustrated in FIGS. 10Cand 10D.

Tabletop Parallelogram Support

A traditional “four-bar parallel arm system” creating a tabletop supportlink parallelogram defined by pivot points 32-38-39-36 is shown in FIGS.6B, 7B and 8B. This four-bar parallelogram holds the tabletop 20 in ahorizontal position, as the linkage 21 moves through its range ofpositions, locked by gas spring 55 whenever the unclamping lever 26 isnot actuated.

A second four-bar parallelogram 31-36-41-42 guides the motion of linkage21. Both of these four-bar parallelograms are shown in FIGS. 6A, 7A, 8A,where they are all shown to be unskewed or unflattened over theoperating range of linkage 21, and their acute angles remain greaterthan 45 degrees throughout this range, assuring effectivecounterbalancing force transmission over the continuous range oftabletop height levels.

In fact, this system may be viewed as a “six-bar system”, in which thesix bars are the rigid cantilever arm 29, defining line 31-32; rigidbell crank 34 defining line 37-36-41; forward link 40; upper link 37; animaginary line 31-VCP (an imaginary virtual center pivot point in space)positioned substantially rearward behind the mechanism; andanother-imaginary line VCP-38, both imaginary lines and point VCP beingshown in FIGS. 1E and 2E.

Imaginary line 31-VCP is parallel to line 32-38 joining the two pivotpoints supporting the tabletop 20. Imaginary line VCP-38 is parallel toline 31-32, joining the two terminal pivot points of cantilever arm 29.

Two additional virtual center pivot points are shown in FIG. 5: VCP_(L),the virtual pivot point for the rotation of the uppermost linkage pivotpoint 38; and VCP_(T), the virtual pivot point for the rear rim oftabletop 20.

The presence of these imaginary virtual center pivot points VCP,VCP_(L), and VCP_(T), all substantially rearwardly behind column 22,base 24 and tabletop 20, produces an extremely compact mechanism with anunusually small form factor. This allows the mechanism to be backed upto the wall of a room, with no tangible components protruding behind it.

Multiple Linkages

It will be readily understood that wherever one single column 22 andlinkage 21 assembly is employed, it may be quite sufficient tocounterbalance a small tabletop. Most wider tabletops will be morestable at all selected levels if they are supported by two column22-linkage 21 assemblies. Indeed, three or more parallel linkage-columnassemblies may be useful for supporting extra-wide tabletops. However,all such multiple column-linkage assemblies should be governed by asingle unclamping lever 26, actuated by a single human user. If twolevers 26 are employed on opposite front corners of the tabletop, theyshould preferably be ganged together, particularly when one centralBLOC-O-LIFT° (“BOL”) is installed. This produces “light”counterbalancing of lighter cargo loads. If two columns 22 areinstalled, each may have its own gas spring piston-cylinder 55,providing “heavy duty” counterbalancing of heavier loads. If each airspring 55 has its own lever 26, actuating either lever will unlock onlyone air spring, and the table will not be free to move until both levers26 are actuated.

A third option provides “super heavy duty” counterbalancing of muchheavier loads, and employs three gas spring units, which should all beunlocked ideally by a ganged pair of levers 26.

Gas Spring Piston-Cylinders without Clamping

In other applications it may be desirable to use a gas pressure springwithout clamping means having the same force characteristics as theStabilus BLOCK-O-LIFT. Uncontrolled extension gas pressure springs alsomade by Stabilus are referred to as NON BLOCKING LIFT-O-MAT gas springsfor lifting, lowering, moving, and adjusting table structures. On theseoccasions, the first or second preferred embodiment is utilized withoutthe user unclamping the gas spring for raising or lowering and wherebythe gas spring could be mounted for automatic full rise or mid positionbuoyancy. A raised linkage system with tabletop could rise like anelevator to reach a shelf where a box container could be placed on thetabletop, which would automatically lower to mid or full down positionas a result of the weight of the box container. A worker loader locatedbelow could remove the box container from the tabletop, and with theweight removed the tabletop would return to its buoyant position or to afully raised position to be re-loaded with another box container.

Without a user controlled locking device, the concern has been expressedthat the tabletop under the force of the gas spring could “snap” up tothe raised position, but the dynamic damping characteristics inherent toStabilus gas springs can be employed to slow the linear motion of thetabletop so as to not create a motion speed danger.

The Third Preferred Embodiment

The third preferred embodiment of the invention relates to the officefurniture field and more specifically to ergonomically designed computerdesks and work stations, including adjustable height computer trainingtables for school classrooms.

Extensive computer use has recently produced wide recognition of theimportance of good ergonomic practices that increase productivity andreduce the occurrence of injury. At the heart of these practices is theadaptation of the work station to the size of the individual to promoteproper work posture.

Most desks are basically stationary and do not move to accommodate thevarious sizes and shapes of individuals. Carpal tunnel syndrome, postureproblems and other maladies are all caused by poor positioning ofcomputer components in relation to the human user, who may be sittingfor long periods of time and doing repetitive tasks.

The emphasis today is to fit the desk surface to the computer user.Today's computer users come in all ages and sizes and desks need toadjust to each individual user. To date, industry has responded withadjustable height keyboard platforms and monitor stands. There are alsowork stations that are adjusted incrementally (during assembly) to fitone desk to one user—they are not dynamically adjustable. There are nowalso adjustable height desks that rise and fall with crank handles orelectric motors. These solutions are cumbersome and expensive.

Adjustable seats that keep the user's feet flat on the floor, keyboardsat elbow height to reduce carpal tunnel repetitive stress, monitors highenough and far enough away to reduce neck and eye strain, etc areprevalent today. However, this is achieved by adding components such asadjustable keyboard trays to existing writing style desks of fixedheight which are most often too high for today's computer use. Smallerfemales and taller males work in compromised postures causing fatigue.Even when the computer components are properly positioned all the otherwork tools such as the mouse; telephone, adding machines, etc. are stillout of proper reach.

The opportunity is to create a height adjustable desk surface that movesboth the keyboard and monitor and everything else on the desk togetherin a quick and easy motion. This would address the sitting needs of anyone individual user—but further, it is important to address the multipleshift work segments where computer work stations are shared by a numberof different size individuals. Hence the work station should adapt toany one individual and to the range of sizes of all the otherindividuals in the workplace as it moves up or down to accommodatedifferent sitting positions.

Height adjustment is important beyond the office—recent concern has beendirected at the growing number of school children being trained to usecomputers in the classroom. These students are seen sitting on highchairs trying to reach the desktop with legs dangling and neck strainingto see the monitor. On average five students share a computer in U.S.classrooms—with the computer desk level fixed and each studentstruggling to adapt themselves to see and use the keyboards andmonitors.

With this third preferred embodiment, illustrated in FIGS. 11, 12, 13,14, and 15A through 18B, a unique desk is achieved that adjusts to thesitting height and reach of all size people. In this design the entiredesktop surface raises and lowers in a dynamic fashion. To allow ease ofadjustment a counterbalancing force compensates for the weight of thedesk top and the computer and other components so the desktop seeminglyfloats up and down when the height adjustment is unlocked by actuatingan unclamping means, and then maintains that position when theunclamping means lever is released.

Therefore it is the primary object of this embodiment of the presentinvention to create a height adjustable work surface that will conformto the proper posture requirements of children and adults.

It is a further object of the present embodiment to have the worksurface level adjustable with relative ease so that its height can bequickly changed in a simple fashion.

It is a further object that the work station is manually controlled andmoves quickly up and down without the use of electric motors or manualcranks.

The height adjustable work station of this embodiment of the inventionutilizes a unique scissors shaped support leg assembly 60 on each sidethat pivots about an axle point 62 to raise and lower the desk heightwhile maintaining the tabletop 61 in a horizontal position.

The crossed legs 63 and 73 comprising one side of the scissors legsassembly 60 have rollers or wheels attached at one end and fixedbrackets at the other. The upper front end of one leg 63 is pivotallybracketed at 64 to the underside of the front edge 65 of the tabletop.The other rear end of leg 63 has a wheel 66 in contact with the floor.The other leg 73 of the same side has a roller 74 in contact with theunderside 67 of the rear portion of the tabletop. On its other front endis a pivotable bracket 76 in contact with the floor. The two legs 63 and73 are attached at center by a pivot 62 to comprise a crossed leg shapedlike an “X”, under each side rim 77 of the table top 61. As the two legspivot about the axle point 62, a scissoring action is created whichchanges their relative angle and hence the height of each “X” shaped legassembly 63-73 supporting one side of tabletop 61.

As the angle of the two legs in relation to each other changes, it canbe seen in FIGS. 15B, 16B and 17B that there is a corresponding relativedistance change between the ends of the two support legs in both thehorizontal and vertical directions. The two leg ends with rollersattached 66 and 74 produce the level change in tabletop 61 as they rollalong the floor and the underside of the desktop. The upper fixedbrackets 64 pivotally mounted to the underside 67 of the tabletop 61 andthe lower brackets 76 resting on the floor remain fixed in positionalong their horizontal planes. When the relative change of angle occurs,the tabletop rises and descends while remaining in a horizontalposition.

To control the angle between the legs, a rolling distance limitingdevice is connected to the rollers on the underside 67 of the tabletop.This device is an unclamping lever 26 on the underside of table 61,preferably under its edge rim 77 near its front rim 65. Lever 26operatively connected by a shutter-type cable 50A to a valve 48 at theoutermost piston end of the gas spring piston-cylinder 52. The outermostend of the extensible piston is also pivotally connected by horizontallypivoting linkage to the rollers 74, as shown in the upper right portionof FIGS. 15A, 16A, 17A, 18A and 18B.

As in the other embodiments, the linearly variable adjustment componentis a gas filled piston-cylinder 55, which produces a counterbalancingforce to compensate for table weight. By closing the gas valve 48 (FIG.9A) the piston-cylinder 52 can be locked in any position along itspiston stoke.

Referring now to the drawings and especially FIGS. 11, 12, 15B, 16B and17B, there are two scissoring leg assemblies 60 of the same dimensionsshown as left and right leg support systems with four floor contacts tostabilize the desk.

When legs 63 and 73 are arranged in a scissors shape, they may beconnected by an axle 62 which is fastened through the two aligned centerpoints 62. As the legs go through the scissors action shown in FIGS. 11to 12, and 15B, 16B and 17B, it can be seen that the fixed points androlling points change distance relative to each other, and allow thetabletop to change height relative to the floor, while maintaining thetabletop in a fixed and rigid horizontal position. Referring now to FIG.14 the table or desk assembly is viewed from underneath in a perspectivebottom plan view. It can be seen in FIG. 15B that as the legs go throughthis scissors action, the horizontal distances increase as the legsspread and the desk lowers. The horizontal distances decrease as thelegs come together in FIG. 17B to raise the tabletop.

In FIG. 14 and FIGS. 15A, 16A and 17A, an axle 72 is supplied connectingthrough the upper ends of legs 73 and mounting the rollers 74. In orderto control the rolling distance, the axle 72 is connected to theunclamping lever 26 positioned near an outer front rim 65 of tabletop61. The roller axle 72 is pivotally connected to a horizontally pivotingbell crank lever 69, whose innermost end is pivotally connected to thelinkage bar 81 at pivot 80. The bell crank lever 69 is shaped like an Land is pivotally fixed at its central point to the underside of thetabletop 61 at pivot point 79. The outer end of the lever 69 is attachedto the moving mount point of a gas valve 48, shown in FIGS. 9A, 15A,16A, and 17A, positioned at the extensible outer piston end of acounterbalance force-generating pressurized gas piston-cylinder 52. Theother end of the gas cylinder 55, preferably the Stabilus BLOC-O-LIFT®,is pivotally fixed at 82 to the underside 67 of the tabletop 61.

Referring again to FIG. 14 and the scissors action of FIGS. 15A through17B—it can be seen that as the tabletop is lowered and the distance ofthe axle 72 from the fixed bracket 64 increases, the reversing action ofthe bell crank lever 69 causes the gas cylinder 52 to compress along itsstroke. This compression provides the force to return the tabletop 61upwards as the compressed gas seeks to resolve its increased storedpressure.

Upright, Forward Projecting or Horizontal Gas Springs

It will be noted that the lockable counterbalancing gas springs 51, 52or 55 incorporated in each of the three embodiments of this inventionprovide the force required to counterbalance the weight of the tabletopand its cargo, in the same way causing the tabletop to float toward itsbuoyant mid-range level whenever the gas spring is unlocked by the user.At such times, each of the tabletops can be raised or lowered by veryslight force applied to it by the user.

When the lever 26 is released by the user, the gas spring is locked,blocking the counterbalancing action and maintaining the tabletop at thelast level selected by the user.

Thus the orientation of the gas spring piston-cylinders' central axis ineach embodiment does not change or affect its counterbalancing action.Upright gas springs 55 (FIGS. 1-4F, 5-8A), forward projecting gassprings 51 (FIGS. 4G-4J) and horizontally-oriented gas spring 52 (FIGS.11-15A, 16A, 17A, 18A and 18B) are not dependent on gravity but onlyupon their pressurized condition to deliver their linearly varyingcounterbalancing force over the entire range of their full strokelength.

It will thus be seen that the objects set forth above, and those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above construction withdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

1. A compact pivoted and counterbalanced table support mechanism providing the user with readily changeable and automatically clamped tabletop heights while maintaining the tabletop level, and counterbalancing the weight of the table and its cargo at a mid range level, while minimizing force applied by the user, when height levels are unclamped, to raise or lower the tabletop through a continuous range of different height levels, comprising: a base, an elongated column upstanding from the rear of the base, a linkage pivoted near the top of the column and protruding forward and upward forming a tabletop-engaging portion, a tabletop overlying the linkage and having an upper surface, a lower surface, a front rim a rear rim, and two side rims joining the front rim to the rear rim, pivot means joining the tabletop to the tabletop-engaging portion of the linkage, an elongated extensible gas spring piston-cylinder having pivots joining each of its ends respectively to the column and the pivoted linkage, and which is normally clamped in any of its extended positions, and at least one manually actuatable unclamping lever mounted on one of the upper or lower tabletop surfaces, along a side rim near the front rim and connected, by a “camera shutter” style cable, to the gas spring piston-cylinder to unclamp it, whereby manual actuation of the unclamping means and application of manual table lifting or lowering force may be simultaneously performed by the individual user.
 2. The counterbalanced table support mechanism defined in claim 1, wherein the gas spring piston-cylinder is provided with two cylinder chambers separated by the piston having a lockable valve which when locked serves to isolate the two chambers, thereby blocking movement of the piston in the cylinder and preventing raising and lowering of the tabletop, and said valve when unlocked serving to connect the two chambers, thereby permitting raising and lowering of the tabletop, said valve being normally closed, and readily opened by manual actuation by the user of the unclamping lever on the tabletop.
 3. The counterbalanced table support mechanism defined in claim 2, wherein the pivot joining the extensible gas spring piston-cylinder to the pivoted linkage is positioned on said linkage at a point where the force provided by the compressed gas in the piston-cylinder substantially matches the component to be counterbalanced of the weight of the tabletop and its cargo at a mid-range position in said continuous range, while it exceeds said component at lower tabletop levels below said mid-range position and is less than said component at higher tabletop levels above said mid-range position, whereby the tabletop floats to a mid-range level, drifts down to the mid-range level from higher levels, and drifts up to the mid-range level from lower levels.
 4. An economical and efficient method for manually adjusting the level of the tabletop in the mechanism defined in claim 2, comprising the steps performed by the individual user of: Determining a changed new tabletop level desired, Manually gripping the unclamping means, thereby opening the valve between the two chambers of the gas spring cylinder, permitting the piston separating the two chambers to move to a different position, simultaneously applying lightweight vertical force manually to move the tabletop to the desired new level, and then releasing the unclamping means, whereby the released unclamping means closes the valve in the gas spring, clamping the tabletop at the desired new level selected by the user.
 5. The mechanism defined in claim 1 wherein said linkage comprises: a cantilever arm, having a rear pivot connecting the arm to the top of the upstanding column, a front pivot connecting the arm to the underside of the tabletop, and an anchor point pivotally joining the arm to the uppermost end of the gas spring piston-cylinder, a forward link having a front end and a rear end, an upper link having an upper end and a lower end, and a bell crank having a central pivot joining it to the cantilever arm, a lower pivot joining it to a front end of the forward link, whose rear end is pivoted to said column, and a rear pivot joining it to the lower end of the upper link, whose upper end is pivotally joined to the underside of the tabletop.
 6. The mechanism defined in claim 5, wherein the cantilever arm is formed as a V-shaped cantilever arm.
 7. The mechanism defined in claim 5, wherein the cantilever arm is formed as a U-shaped cantilever arm.
 8. The mechanism defined in claim 5, wherein the anchor point joining the gas spring's uppermost end is positioned on the cantilever arm at a point between its rear pivot and the central pivot joining the bell crank to the cantilever arm.
 9. The mechanism defined in claim 5 wherein the two end pivots of the upper link form a first parallelogram with the bell crank's central pivot and the front pivot of the cantilever arm.
 10. The mechanism defined in claim 5 wherein the two end pivots of the forward link form a second parallelogram with the rear pivot of the cantilever arm and the central pivot of the bell crank.
 11. The mechanism defined in claim 9, wherein the ends of the upper side of the first parallelogram, delimited by the upper end pivot of the upper link and the cantilever arm's front pivot are respectively adjustable to skew the first parallelogram, whereby the tabletop may be shifted out of a horizontal orientation if desired by the user.
 12. The mechanism defined in claim 5 wherein, during raising and lowering travel of the tabletop through its continuous range of different height levels, the rear rim of the tabletop, and the pivot point joining the underside of the tabletop to the upper end of the upper link, both move along circular arcuate paths having equal radii of curvature about respective virtual center points positioned behind all parts of the mechanism by substantial distances, whereby the mechanism itself occupies a minimum volume and achieves a compact minimum form factor.
 13. The mechanism defined in claim 8 wherein the components of the linkage defining the first parallelogram are dimensioned to make the first parallelogram substantially rectangular for a mid-range level of the tabletop, whereby the acute angles at the apices of the first parallelogram are no smaller than 45° at the lowermost level and at the uppermost level of the tabletop, thus avoiding flattening of the first parallelogram and assuring effective force transmission by the linkage throughout the continuous range of tabletop height levels.
 14. The counterbalanced table support mechanism defined in claim 1, wherein each manually actuatable unclamping lever is mounted under the side rim of the tabletop, near its front rim, where it is conveniently presented for gripping by the human user.
 15. A compact pivoted and counterbalanced table support mechanism providing the user with readily changeable and automatically clamped tabletop heights while maintaining the tabletop level, and counterbalancing the weight of the table and its cargo at a mid range level, while minimizing force applied by the user, when height levels are unclamped, to raise or lower the tabletop through a continuous range of different height levels, comprising: a linkage supported by an underlying floor, a tabletop overlying the linkage and having an upper surface, an underside surface, a front rim, a rear rim, and two side rims, a pair of downslanting legs each having an upper end pivotally anchored on a first transverse axis to the tabletop's underside near its front edge, and each having a lower end pivotally supporting a wheel rotatable on a second transverse axis, a pair of upslanting legs each having a lower end pivotally anchored to a floor-supported bracket on a third transverse axis directly below said first transverse axis, and each having an upper end pivotally supporting a roller supporting said underside surface of said table rotatable on a fourth transverse axis directly above said second transverse axis, one downslanting leg of each pair being adjacent to an upslanting leg, the mid-points of both adjacent legs being pivotally joined on a fifth transverse axis, the rollers being positioned and connected for ganged rolling motion toward and away from the tabletop's rear rim, a link having a rear end connected to said ganged rollers and having a front end, a bell crank having an inner end, an outer end, and a central pivot point pivotally connected to the underside of the tabletop, the inner end also being pivotally connected to the front end of said link, and the outer end having a pivot point thereon, an extensible gas spring piston-cylinder having pivots joining each of its ends respectively to a fixed point and to the outer end of said bell crank and which is normally clamped to block telescoping movement of the piston in the cylinder in any of its extended positions, and manually actuatable unclamping lever means mounted on one of the upper or lower tabletop surfaces, and connected, by a “camera shutter” style cable, to the gas spring piston-cylinder to unclamp it, whereby manual actuation of the unclamping lever means and application of manual table lifting or lowering force may be simultaneously performed by the individual user.
 16. The compact table support mechanism defined in claim 15, wherein the gas spring piston-cylinder is provided with two cylinder chambers separated by the piston having a lockable valve which when locked serves to isolate the two chambers, thereby blocking movement of the piston in the cylinder and preventing raising and lowering of the tabletop, and said valve when unlocked serving to connect the two chambers, thereby permitting raising and lowering of the tabletop, said valve being normally closed, and readily opened by manual actuation by the user of the unclamping lever means on the tabletop.
 17. The compact table support mechanism defined in claim 15, wherein the gas spring piston-cylinder is positioned substantially horizontally near the underside surface of the tabletop, and wherein said fixed point is a point on the underside surface of the tabletop.
 18. The compact table support mechanism defined in claim 15, wherein said bell crank is dimensioned with unequal ends, the outer end being shorter than the inner end, whereby the central pivot point is closer to the outer end pivot point and farther away from the inner end pivot point.
 19. The compact table support mechanism defined in claim 15, wherein the central pivot point and the inner and outer end pivot points of the bell crank and the fixed point are all adapted to be repositioned, whereby the mechanical advantage may be selectively altered to change the relationship of the linearly decreasing gas spring force, produced by telescoping extension of the piston, to the changing component of tabletop weight at different level positions as affected by gravity.
 20. A compact pivoted and counterbalanced table support mechanism providing the user with readily changeable and automatically clamped tabletop heights while maintaining the tabletop level, and counterbalancing the weight of the table and its cargo at a mid range level, while minimizing force applied by the user, when height levels are unclamped, to raise or lower the tabletop through a continuous range of different height levels, comprising: a linkage supported by an underlying floor having pivoted components and protruding upward forming a tabletop-engaging portion, a tabletop overlying the linkage and having an upper surface, a lower surface, a front rim, a rear rim, and two side rims joining the front rim to the rear rim, pivot means joining the tabletop to the tabletop-engaging portion of the linkage, an elongated extensible gas spring piston-cylinder having two ends, with pivots joining one of its ends respectively to a fixed point and the other end to the pivoted linkage, and which is normally clamped in any of its extended positions, and at least one manually actuatable unclamping lever mounted on one of the upper or lower tabletop surfaces, and connected, by a “camera shutter” style cable, to the gas spring piston-cylinder to unclamp it, whereby manual actuation of the unclamping lever and application of manual table lifting or lowering force may be simultaneously performed by the individual user.
 21. A compact pivoted and counterbalanced table support-elevator mechanism providing the user with readily changeable tabletop heights while maintaining the tabletop level, and counterbalancing the weight of the table and its cargo at a topmost level, while minimizing level changing speed when height levels are changing, to raise or lower the tabletop through a continuous range of different height levels, comprising: a base, an elongated column upstanding from the rear of the base, a linkage pivoted near the top of the column and protruding forward and upward forming a tabletop-engaging portion, a tabletop overlying the linkage and having an upper surface, pivot means joining the tabletop to the tabletop-engaging portion of the linkage, an elongated extensible gas spring piston-cylinder having pivots joining each of its ends respectively to the column and the pivoted linkage, and which has no clamping or locking capability in any of its extended positions, whereby the tabletop without cargo automatically rises, responding to the counterbalancing force supplied by the gas spring piston-cylinder to a high loading level, for receiving a predetermined cargo whose extra weight exceeds the counterbalancing force, causing the tabletop to descend to an unloading level, and after unloading the tabletop automatically repeats the cycle. 